The present invention relates to mandrel systems for supporting a workpiece during manufacturing operations, and more particularly, to rotatable mandrel systems for holding a container such as a one-piece can body member during a coating or decorating operation on a conventional coating or decorating machine.
In high speed continuous coating or decoration of one-piece aluminum or steel can body members, the can body members are supported on a plurality of circumferentially spaced mandrel assemblies carried by a continuously rotating mandrel wheel for engagement of the outer peripheral can surface with ink transfer blanket segments on a rotating blanket wheel of a decorator machine or for engagement with a coating applicator roll of a coating machine. The mandrel wheel and mandrel assemblies of such coater and decorator machines are of generally similar construction. Decorators of this general type are described and shown in the following United States patents, the disclosures of which are incorporated herein by reference: Sirvet 4,037,530; McMillin et al. 4,138,941; Dugan, et al. 4,222,479; Stirbis 4,267,771; Hahn 4,441,418; Stirbis 4,445,431; Stirbis 4,491,068; Stirbis 4,498,387; and Stirbis 4,509,555. Such decorator apparatus is continuously operated by a motor means and a drive means with the various wheel means rotating synchronously. The construction and arrangement is such that each can member is decorated along approximately 20 degrees of each 360 degree revolution of the mandrel wheel means when in contact with a blanket segment. Decorator apparatus of this type are operable between relatively low speeds of approximately 500 cans per minute and relatively high speeds of 1200 to 1400 or more cans per minute.
In general, each of the mandrel assemblies comprise a central support spindle shaft means attached to and carried in a circumferential path by the rotatable mandrel wheel. A mandrel means is rotatably mounted on each of the spindle shaft means by suitable bearing means. Mandrel assemblies of this type are shown and described in the following United States patents, the disclosures of which are incorporated herein by reference: Stirbis 4,267,771; Sirvet 4,037,530; Demierre 3,710,712; Cohan 3,388,686 and Zurick 3,356,019.
In the past, the mandrel means has been made of precision machined metallic steel alloy material or in some cases, plastic materials, such as Nylatron, have been utilized. There are several problems associated with prior art mandrel systems. A major problem is that the prior art mandrel systems are subject to a high degree of wear and must be periodically replaced at substantial cost. There may be substantial loss of production when the mandrels become unsatisfactory due to inadvertent production of defective cans and lack of production during machine down-time when unsatisfactory mandrels must be replaced. Another problem is that the mandrels must be dimensionally accurate with relatively close tolerances to properly fit inside the cans and also have accurate alignment on the mandrel wheel. Many prior art mandrel designs require more high performance costly bearing units and relatively costly support structure. In addition, weight of the mandrel is a limiting factor in high speed operations so that relatively light-weight mandrels are preferable to relatively heavy-weight mandrels.
While a Nylatron mandrel is light weight and enables easy loading and unloading of the can member thereon, the life expectancy is about five weeks when used 24 hours per day for 7 days per week at 1000 can per minute printing speeds. A diameter of 2.576 inches will deteriorate to 2.568 inches in a five week period due to wear. The mandrels must then be replaced as this diameter variance will no longer allow proper printing. Diameter variance is also caused by expansion and shrinkage due to variations in the plant temperature. The plant ambient temperature may fluctuate as much as 50 degrees F. in a day. In addition, abrasion resistance is also proportional to temperature. The thermal coefficient of expansion of Nylatron is 20.times.10 to minus sixth power. A Nylatron plastic material will cold flow under pressure and must, therefore, be supported by other means to make it suitable for a mandrel. Additional bearings are added to give center span support. A four bearing system is currently used on one commercially available printer. The more bearings that are used, the more alignment problems that are encountered with increased cost of not only the mandrel, but also the spindle. Of course, additional parts add additional mass. During printing, the mandrel position must be altered and mandrel mass therefor may be a limiting factor for high printing speeds. The use of Nylatron has been attractive because a Nylatron mandrel by itself typically weighs approximately 1.5 pounds and with its additional required support hardware approximately 2.1 pounds.
Steel alloy materials are used to obtain longevity and dimensional stability. Only two bearings are required. However, a steel mandrel will weigh approximately 4.75 pounds. Steel mandrels are also subject to coating with oxidized aluminum from the aluminum cans which adheres to the steel mandrel surface and, in turn, damages the can. Cans used for soft drink beverages containing phosphoric acid, such as cola beverages, are particularly vulnerable to residue such as oxidized aluminum which may be transferred to the inside of the can and adversely affect beverage taste. High speed coater/decorator machines operate at about 1200 cans per minute, sustained production, speeds and may operate at as high as 1600 cans per minute. It is now contemplated that production speeds of 1600 to 2200 cans per minute may be attained so that mandrel weight becomes a more critical factor. However, when such speeds are reached, the wear life of the mandrels will decrease and a plastic mandrel will have a useful life of about 3 to 3.5 weeks or less and down time from defects caused by dimensional changes, etc. will be an increasing production problem.